(1) Field of the Art
This invention relates to a switch device comprising a thermally responsive element such as bi- or tri-metallic disc cantilever supported within a metallic enclosure in a manner to have a movable contact at its free end in making and breaking contact relationship with a fixed contact secured to a suitable support arm, and more particularly concerns a thermally responsive switch device having a central dish-shaped portion to cause the thermally responsive element to reverse its curvature with snap action in response to the ambient temperature or the like.
(2) Description of the Prior Art
In this type of a thermally responsive switch, a projection depends from the upper inner side of the enclosure to engage with the upwardly curved dish-shaped portion of the thermally responsive disc to exert a pressure from the movable contact to the fixed contact in order to eliminate initial creep from the disc upon its hot and cold snap movement according to elevated and lowered temperature.
However, such movement always accompanied by welding force, albeit slightly, due to arching between the movable and the fixed contacts, subjecting the disc to reaction of the welding force at the proximity of the cantilever end. The reaction tube exerted upon the disc allows bending moment about its cantilever support end to result in its increased deformation.
One of the problems arising from the above is to render the hot and cold snap temperatures in variance from intended ones, otherwise to allow the disc for creep so as to deteriorate its endurance.